/*
 *   This program is free software: you can redistribute it and/or modify
 *   it under the terms of the GNU General Public License as published by
 *   the Free Software Foundation, either version 3 of the License, or
 *   (at your option) any later version.
 *
 *   This program is distributed in the hope that it will be useful,
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *   GNU General Public License for more details.
 *
 *   You should have received a copy of the GNU General Public License
 *   along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

/*
 *    SerializedInstancesLoader.java
 *    Copyright (C) 2002-2012 University of Waikato, Hamilton, New Zealand
 *
 */

package weka.core.converters;

import java.io.BufferedInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.ObjectInputStream;

import weka.core.Instance;
import weka.core.Instances;

/**
 * <!-- globalinfo-start --> Reads a source that contains serialized Instances.
 * <p/>
 * <!-- globalinfo-end -->
 * 
 * @author <a href="mailto:len@reeltwo.com">Len Trigg</a>
 * @version $Revision$
 * @see Loader
 */
public class SerializedInstancesLoader extends AbstractFileLoader implements BatchConverter, IncrementalConverter {

    /** for serialization */
    static final long serialVersionUID = 2391085836269030715L;

    /** the file extension */
    public static String FILE_EXTENSION = Instances.SERIALIZED_OBJ_FILE_EXTENSION;

    /** Holds the structure (header) of the data set. */
    protected Instances m_Dataset = null;

    /** The current index position for incremental reading */
    protected int m_IncrementalIndex = 0;

    /**
     * Returns a string describing this object
     * 
     * @return a description of the classifier suitable for displaying in the
     *         explorer/experimenter gui
     */
    public String globalInfo() {
        return "Reads a source that contains serialized Instances.";
    }

    /** Resets the Loader ready to read a new data set */
    public void reset() {

        m_Dataset = null;
        m_IncrementalIndex = 0;
    }

    /**
     * Get the file extension used for arff files
     *
     * @return the file extension
     */
    public String getFileExtension() {
        return FILE_EXTENSION;
    }

    /**
     * Gets all the file extensions used for this type of file
     *
     * @return the file extensions
     */
    public String[] getFileExtensions() {
        return new String[] { getFileExtension() };
    }

    /**
     * Returns a description of the file type.
     *
     * @return a short file description
     */
    public String getFileDescription() {
        return "Binary serialized instances";
    }

    /**
     * Resets the Loader object and sets the source of the data set to be the
     * supplied InputStream.
     *
     * @param in the source InputStream.
     * @throws IOException if there is a problem with IO
     */
    public void setSource(InputStream in) throws IOException {

        ObjectInputStream oi = new ObjectInputStream(new BufferedInputStream(in));
        try {
            m_Dataset = (Instances) oi.readObject();
        } catch (ClassNotFoundException ex) {
            throw new IOException("Could not deserialize instances from this source.");
        }

        // close the stream
        oi.close();
    }

    /**
     * Determines and returns (if possible) the structure (internally the header) of
     * the data set as an empty set of instances.
     *
     * @return the structure of the data set as an empty set of Instances
     * @throws IOException if an error occurs
     */
    public Instances getStructure() throws IOException {

        if (m_Dataset == null) {
            throw new IOException("No source has been specified");
        }

        // We could cache a structure-only if getStructure is likely to be called
        // many times.
        return new Instances(m_Dataset, 0);
    }

    /**
     * Return the full data set. If the structure hasn't yet been determined by a
     * call to getStructure then method should do so before processing the rest of
     * the data set.
     *
     * @return the structure of the data set as an empty set of Instances
     * @throws IOException if there is no source or parsing fails
     */
    public Instances getDataSet() throws IOException {

        if (m_Dataset == null) {
            throw new IOException("No source has been specified");
        }

        return m_Dataset;
    }

    /**
     * Read the data set incrementally---get the next instance in the data set or
     * returns null if there are no more instances to get. If the structure hasn't
     * yet been determined by a call to getStructure then method should do so before
     * returning the next instance in the data set.
     *
     * @param structure ignored
     * @return the next instance in the data set as an Instance object or null if
     *         there are no more instances to be read
     * @throws IOException if there is an error during parsing
     */
    public Instance getNextInstance(Instances structure) throws IOException {

        if (m_Dataset == null) {
            throw new IOException("No source has been specified");
        }

        // We have to fake this method, since we can only deserialize an entire
        // dataset at a time.
        if (m_IncrementalIndex == m_Dataset.numInstances()) {
            return null;
        }

        return m_Dataset.instance(m_IncrementalIndex++);
    }

    /**
     * Main method.
     *
     * @param args should contain the name of an input file.
     */
    public static void main(String[] args) {
        runFileLoader(new SerializedInstancesLoader(), args);
    }
}
